1. Field of the Invention
This invention is in the field of fluorine chemistry and more particularly in the field of direct fluorination.
2. Description of the Prior Art
The class of polymers known as fluoropolymers are known to exhibit outstanding high temperature properties and are also unusually chemically inert. Because of such properties, they have become extremely valuable in applications where severe environmental factors are encountered.
There have been many problems encountered in producing certain fluoropolymers. One problem is the difficulty in carrying out fluorination reactions. Whereas many compositions can be directly chlorinated or brominated, it has been recognized that fluorine is dissimilar to these halogens in regard to direct halogenation. See McBee et al., U.S. Pat. Nos. 2,533,132 and 2,614,129. In fact, even though direct fluorination is a highly desirable process, prior attempts to use direct fluorination have often produced low to mediocre yields. Additionally, the yields are known to decrease as the molecular complexity of reactants becomes greater, therby making direct fluorination of polymers an even more difficult matter. It is stated in one literature article, for example, that the yield of required fluorocarbon decreases as the molecular complexity of a hydrocarbon precurser increases, and it is difficult to fluorinate hydrocarbons above C.sub.10 without extensive decomposition occurring. See R. E. Banks, "Fluorocarbons and Their Derivatives", Oldbourne Press, London, p. 7 (1964).
It has been theorized that certain perfluoroether oligomers having terminal carboxylic acid or acid fluoride (--COF) functionalities would have outstanding properties for a number of utilities. Perfluorinated polyethylene oxide having more than two or three repeating ethylene oxide units in the polymer chain, for example, would be expected to be extremely stable, chemically inert, have a favorable glass transition temperature, and have lubricating properties. An oligomer such as this, having terminal functional groups, could be used as a comonomer in polymers wherein it was desired to add flexibility and stability.
Much research has been directed to synthesizing perfluorinated polyethylene oxide. One of the methods used so far was the polymerization of tetrafluoroethylene oxide together with various techniques to simultaneously functionalize the terminal groups. These efforts have met without much success, although some species have been prepared having as many as three or four repeating ethylene oxide units. Nevertheless, these materials fall below the degree of polymerization desired for most applications.